<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
// 求1+2!+3!+...+20!的值
        
        var total = 1;
        for(b = 1;b<=20;b++){
            var num = 1;
            //  total *= num; 
            //  console.log(total);
             for(a = 1;a<=b;a++){
                num *= a; 
             }
             total +=num;
             
        }
        console.log(total);  
    </script>
</body>
</html>